The present invention relates generally to an apparatus for twisting strand while winding the strand onto a rotating bobbin, and more particularly, to such an apparatus wherein the speeds of rotation of the bobbin and of a concentrically rotating strand hook are controlled to maintain a preselected strand tension.
In one widely used method of processing natural and synthetic fibers to form yarn, thread or other type of strand, sliver is supplied to a fly frame for transformation into a loosely twisted strand termed "roving." The roving is then supplied to a spinning frame where it is led through drafting rolls for transformation of the roving into strand having a diameter less than the diameter of the roving. The degree of attenuation or "draft" imparted to the roving depends on the type of yarn or thread being processed, e.g., finer yarns require a smaller diameter roving, and more draft.
After passing through the drafting rolls, the strand is fed through a strand guide to a rotating bobbin or spool onto which the strand is layered. The guide causes the strand to be supplied to the bobbin parallel to the axis of rotation thereof for twisting. Between the strand guide and bobbin, the strand passes through one type of twisting and winding apparatus known as a "ring and traveller," comprising a traveller slidably mounted on a ring located coaxially about the bobbin. As the strand is taken onto the rotating bobbin, the traveller, pulled by the strand, is caused to slide along the ring, orbiting the bobbin. Due to windage and friction, the speed of the traveller is somewhat less than the speed of rotation of the bobbin. The speed differential between the bobbin and traveller causes the strand to be wound onto the bobbin while the rotation of the traveller with respect to the fixed strand delivery rolls imparts twist to the incoming strand. The amount of twist imparted to the strand is determined by the lineal feed rate of the strand and the angular velocity of the revolving strand guide, e.g., traveller. Tension in the strand is determined by several factors, including traveller speed, friction, wind resistance and the angle of strand pull relative to the tangential path of the traveller.
During winding of the strand onto the bobbin, either the bobbin or the ring is made to reciprocate along the common axis of rotation. As a result, the strand is wound onto the bobbin in successive layers where each layer consists of strand which is laid onto the bobbin in a uniform helical pattern. This uniformity is achieved by synchronizing speed of rotation of the bobbin to the axial movement of the bobbin or ring.
In another type of twisting and winding apparatus, the strand is guided through a rotating flyer as the strand is wound onto the rotating bobbin. Both the bobbin and flyer rotate at a high rate of speed, but in conventional apparatus, the bobbin lags behind the flyer thereby winding the strand onto the bobbin. The flyer also imparts twist to the strand because one end of the strand is constrained from rotation at the point from which it is fed from the delivery rolls. In order to cause the strand to be wound onto the bobbin with uniform tension, the lineal speed of the strand as it is delivered to the bobbin must be maintained constant. Also, the lineal take-up rate of the bobbin must, at all times, equal this constant delivery rate. This requirement calls for a speed differential between the bobbin and flyer that is maximum as the first layer of strand is being wound onto the bobbin, and decreases with each successive layer. In the past, the speed differential has been step-wise decreased during each traverse of the bobbin using a cone drive and pulley belt-type of variable speed drive operating through relatively complex gearing. Each traverse causes an incremental shift of the pulley and belt and a corresponding change in the drive ratio and the bobbin drive and the flyer drive.
There still exists a need for an apparatus for twisting and winding strand onto a bobbin without the requirement of complex variable speed drive mechanisms, as is the case with flyer frames, and, in the case of ring spinning, without the requirement of using ring travellers, with all the problems attendant thereto.